Dr. Hibberd's answer:
 

Simple linear scars often become less evident over time, and evolve from a reddish hue to a pale streak. This process though can take up to seven years to evolve fully, especially with larger scars. When scars or keloids are present, it is always wise to have any healing supervised by a dermatologist or a plastic surgeon.
 

Some scars can be reduced by local injection of cortisone into the scar. Scars can be partially erased by dermabrasion, excision, and other technques. Sometimes surgical techniques, or skin grafting, is needed to obtain good results.

A more appealing route for many is the application of a silicone film containing a topical dressing that is to be applied to a closed scar (that has already healed to skin closure) to help fade it. Otherwise you are left with make-up and topical disguising agents.